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What is it?

Barmah Forest virus disease is a common and important cause of arthritis in Australia.The virus was first isolated from mosquitoes trapped in the Barmah Forest of northern Victoria. Human infection is acquired through mosquito bite. Most people infected with the virus do not show clinical signs or symptoms and go unnoticed. Clinical disease occurs most commonly in adults from 20 to 50 years of age.

The incubation period (time between the bite by a mosquito carrying the virus and the start of symptoms of infection) is 7-9 days on average but may range between 4-14 days. The usual symptoms are joint and muscle pain, fever and in some cases a rash, headaches and fatigue. The fever may be mild and go unnoticed. The rash involves the chest, back and limbs. The joints of the legs and hands are most often affected and back pain is also relatively common. The illness tends to subside over time with occasional relapses of joint pain and fatigue.

Most cases of infection occur in coastal regions with large populations of the mosquitoes that may carry the virus but cases are occasionally reported in inland areas. Australia is the only country in which BFV has been identified. The disease is present in northern Queensland, the Top End of the Northern Territory and the far north of Western Australia. Further south, infections rates are lower but outbreaks still occur in coastal regions.

In recent years the number of reported cases has increased substantially. Disease activity tends to be epidemic following spring and summer rains, because carrier mosquitoes are more likely to breed under such conditions.

The symptoms of the disease are similar to those of the Ross River virus. It is generally considered that the Barmah Forest virus causes a milder illness than Ross River virus and is more likely to cause a rash. However, the similarities between the Barmah Forest virus illness and those of the Ross River virus disease indicate the need to confirm that the correct diagnosis has been made using laboratory tests.

Last Review Date: August 1, 2018

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